Paraffin isomerization process



June 19, 1945. R B MASON PARFFIN ISOMERIZTIN` PROCESS Filed Oct. 2l, 1941 buano dav-both branched chain structures.

Patented June 19, 1945 PARAFFIN lsoMEmzA'rroN Pnoosss Ralph Burgess Mason, Baton Rouge, La., assignor o to Standard Oil Development Company, a corporation of Delaware Application October 21,1941, Serial No. 415,859V 9 claims. (o1. 26o-1683.5)

The present invention relates to the process of isomerizing straight chain hydrocarbons, in parl ticularUn-butane or n-pentane to produce the corresponding isoparafns of `branched chain structure, in particular isobutane and isopentane.

It has heretofore been known to employ the various Friedel-Crafts type catalysts, such as, for example, the chlorides and bromides of aluminum, iron, zinc, and the like as catalytic agents `for effectuating the isomerization of normal parains of `at least four carbon atoms per molecule to isoparaflins having the same number of carbon atoms per molecule. These catalysts have heretofore been employed with promoters, such as,

for" example, water, the hydrogen halidespsuch l as,`hydrogen chloride, hydrogen bromide, hydrogen fluoride, the free halogens, such as, chlorine and bromine, the alkyl halides, such as, methyl, ethyl, propyl or butyl chlorides or bromides, the alkyl polyhalides, such as, for example, chloroform, carbon tetrachloride, and the like. The iso-paralnic hydrocarbon products present various physical and chemical characteristics and nd utility in general by reason of their` having Heretofore, various difficulties have been encountered in carrying out normal paraffin isomerization processes, in particular those employing aluminum chloride as the activating agent, and becauseit-l hasbeen found that these catalysts are not easily controlled, particularly in their activating tendencies, diffrculties arise in carrying out a continuous liquid phase operation. Because of the problem of catalyst segregation in the products in substantial amounts, the clogging of lines and valves with solid catalyst deposits and byreason of the tendency of aluminum chloride, for` example, to dissolve or become entrained` in the hydrocarbon mixture and to be `precipitated out upon-a subsequent cooling of the mixture, an unusually high degree of loss of catalyst is obtained in the cornmercial unit. In other words, before` the full activity of the catalyst has been utilized for isomerization, a substantial portion of the catalyst has `been removed from the reaction zone due to entrainment and solution in the reactants and reactant mixture. It has previously been proposedto solve the problem of `catalyst solution in the hydrocarbonsby subjecting .the eflluent from the isomerization reactor to a shock chilling so as to effectively precipitate out in a suitable manner the dissolved and entrained aluminum chloride, for example. This method, however, has proved to be somewhat cumbersome in operation due to the fact that it becomes necessary to remove solid material from the settler or lilter and to convey it back to the isomerization reactor or to utilize the same in some other manner. The process of the present invention is designed to `avoid the cumbersome handlin'g `of solid4 material which'has heretofore been thought to be necessary in order to conserve the overall o.

aluminum chloride consumption. o

It is an object of the present invention to `carry out the isomerization of normal paraffns to isoparaflins in the presence of aluminum chloride and a promoter, ifl desired, in such a manner as to avoid the operating ineiciencies arising by reason of aluminum chloride becoming dissolved in the? hydrocarbons contacting the same inthe isomerization zone.

It is another, object of the invention to more fully utilize the activity of the catalyst inherently present in the eflluent from an isomerization reactor. Y

, It is a further object of thejinventionto convduct a continuous isomerization process employ.- ingalumnum chloride, as, the catalyst in such a `manner as to cause afreeand uninterrupted flow of the reactants through theunit without substantially-altering the activity of the main body ofthe aluminum chloride and yet to completely and fully realize the full value andfull activity of substantially all of the aluminum chloride for isomerizing normal parafns `to isoparailins.

These objects aswell as others which will be apparent` upon Aa fuller understanding of the invention, as o hereinafter 4more specifically Vdescribed, `are accomplished by operatingthe usual co'mme'rcial equipment `for `the isomerization of normal paraftins of at least 4 carbon atomsper molecule in the presence `of aluminum :chloride wherein the efuent from"the` isomerization reactor or reactors upon leaving the said reactor or reactors is subjectedwto a temperaturesubstan- `tially higher than that maintained 'in theisomerization reaction zone for` a short period of time so `that the entrained and dissolved aluminum chloride has an opportunity to activate the isomerization reaction under increased activity conditions fora short period of `time and, at the same time, resulting inthe substantially complete usage of the alurninumchloride contained thereinto such an extent that its subsequent recovery in the present process becomes unnecessary and uneconomical, as will be shown hereinafter. By

vpracticing the process of the present invention,

improved conversions to .the desired products are obtainable `and at the same` time the mainbody of the aluminum chloride present in the isomerization reaction zone suffers no excessive degradation, such degradation and` increased activity being conned to that small amount `'of aluminum chloride .which is entrained `or dissolved by the efuent from the` isomerization reactor.

In general, the eluent from the isomerization reactor is heated toa temperature between about 25 F. and about 200` F." more than the temperature maintained inthe isomerization reactor from which the` eluent emerges,` `preferably this o about 0.5 and' about 3 hours.

about 50 F. and 100 F. The time of contact of the eiiuent fronr the'risomerization,reaction.zone

tween about and about 50% of thetime of 'at the increased temperature is maintained be.- l

contact under which the feed stock is maintained! in the'isomerization reactor proper preferably,

between about 10% and about 25% ofthis isomerization reactor time of contact. The heating zone through which the reacted.;` mixture from; the;

isomerization reactor passes may be of any suitable design, such as, for example, adirectiired furnace, a steam coil running superheated'st'eam,

if necessary, or any other similar typeo heat' exchange equipment. Care,`however,y should be taken in subjectingthe eiiiuent from the isomerization reactorr t'o thel increased, temperatures to carefully correlate, the time of contact andi the increasedftemperaturesoas to substantially; completely utilize the catalytic activity oftheA dissolved" or entrained aIuminumchIOride, while,lat the same time, avoiding the subjectingofl the'ef.- iiuent from the isomerization zone to any more severe reaction. conditionsithan are required' to accomplish utilization of" the aluminum chloride contained thereinsincemore severe'reaction conditions'onlyfserve to increase." the crackingjtendencyk of` the hydrocarbon constituents oi" the effluent thereby lowering the overall yields of the desired isomeric parains.

The isomerization reaction conditions inthe presence of 'aluminum chloride, and* promoter are more orA less4 wellv known; however, briefly',l they y maybe set' forth' as follows, In general,v a' time of contact between about 1/21 andi 1,0; hours, prefi erably'between about I and;4 hours with a temperaturerA between about`F.-1and about 300 F. isLu'sed. A catalyst concentration between about 2% and about; 100% by weight of the normal parains, preferably between about 15%- and about..4'0%, anda catalyst promoter concentration oi between about'2%' and about 25%', pref'- rerably` between about 3% and about `12% are suitable except, for fixed` bed Operation. It. is realized; of coursethat these'freaction conditions maybe variedt over a considerable range depending upon thevparticular feed` stock employed' and the proper correlation oi conditionsl therefor. Thus,` for example, in the isomerization of n-butane the reaction. is usually carried out. at tem.- peraturesl between aboutv 150or F; and about. 275 F. witha catalyst concentration depending upon the type of reaction. employed' of'between about 10% andv about 100%, although where` a bed type of. catalyst operation is employed, the concentration is'. ordinarily much greater, even up to D-400 The amount of promoter, for example, hydrogen halide employed"` is generally between about 3% and about 25% for n-butaneisomerization, while the contact time varies between Iny the case of n-pent'ane less drastic.` reactionv conditions are maintained although the amounts of promoter and catalystsare substantially thev same as those employed in' the case ofn-butane. The temperatureg. however, is generally maintained' between about' 40' F.' and aboutj75` Fpand. the time of` contact. is maintained between about 1 andl about 2' hours. Likewise, less drastic conditionsv are employed for the isomerization of straight run naphthas. l

It' is particularly' desirablel in practicing' the process oftlvel present invention to: maintain at leastsu'icient superatmospheric' pressure to in.- sure liquid phase4 operation of" the process; thus,

for example, when employing n-butane, pressures ranging up to 1000 lbs./sq.in. may be employed, although,l inI general, pressures-no higher than 400. lbs./sq'.in. are adequate. One convenient method of obtaining increased pressure comprises "introducing gases such as methane or preferably molecular hydrogen into the system. The halogen-containingy promoters previously` mentioned, for. example,A hydrogen chloride, also assist in maintainingthe;superatmospheric pressures. Not only' does the; hydrogen help to maintain the superatmospheric pressures heretofore mentioned" but it likewise has been found to suppress to. an certain extent the tendency toward cracking, particularly where 'the discharged reactant able feed stocksyin general', any hydrocarbon mixturev composedipredominantly of` straight chain parafhnscontaining atleast 4 carbon atoms per molecule is suitable as` a feed' stock `for the present process.y

The isomerizatitm` reactor may be of any-conventionalrdesign such asthat ordinarily employed for contacting a solidv catalystwith Y either liquids Y or'vapors; thus, for example, a bed` type reactor driven propellers, jets of restricted internal di-l may be employed'l such- ,asy a tower filled with aluminum chloride eitherv asV lumps, powder, granules; ory the like, or with aluminum chloride supportedor impregnated on a suitablecarrier such as puiniee,` kieselguhr;- bentonite, montmorillonite, silica andl alumina gels, activated carbon, Porocel, alumina bauxite, and the like. It is desirable; to insure adequatereaction in the is'omerization zone, that thenormal parafhns be intimately and thoroughly contacted with the catalyst; This mayY be accomplishedA by passing through a bed, or by agitation Where smaller amounts of catalyst are present, such as in a slurry withV therea'ctants', also vby'mechanical agi tating means suchv as turbo mixers, mechanically ameter and' similar devices designed to -accomplish intimate contact and intensive agitation.

In order toimore fully,` understand the process of the invention, reference may be had' to the accompanying drawing which diagrammatically `and in sectional elevation proposes a iiowplan showing a suitable plant unit for carrying out the process. In order to simplify the drawing, it will be described in connection with n-butane as a feedstock, an aluminum chloride bed as the-catalyst; mass in the reaction zone and hydrogen chloride 'as' aA promoter. v

N-butane'which may be premixed with hydro* gen chloride is introduced'under` suhicient pressure'to maintain it in the liquid phase through lineA 2A into heater 4 where' it is preheatedito the desired' reaction temperature, for example 150?,

to,225-F. The liquid butanerunder this pressure is then conducted by means of'linev 3 into reactor 5.v Within or in close proximity to inlet line=v3 andthe outlet line 'l are small masses of glass Wool, rock` wool` or other suitable material' 6` de'- considerably. ,The rate of throughput of the n-butane through reactor is such as to give a contact time in the reactor of about 0.5 to 2 or even 3 hours. `Hydrogen `halide may be introduced into the system through line I2 and conducted by meansof line II into contact withthe n-butane entering the system through line 2.

The eiiluent from reactor 5 is conducted through line 1 by means of a pump (not shown) or to a storage tank or intermediate storage drum and from there by means of a pump (not shown) it is conducted at an independent rate of `flow through a heating coil 3 maintained'at a temperature of about 250 F. to 300 F. for a period of time of about to 30 minutes depending upon the degree of cracking which the hydrocarbons undergo. During such treatment, of course,` the degree of cracking should be maintained `at a minimum and, as explained heretofore, this may be accomplished by-the maintenance of a substan-` tially positive pressure of molecular hydrogen in the system. The effluent from heater 8 is conducted by means of line S into a stripping tower I0 which may be maintained undera reduced pressure from .that maintained in the reactor 5 rectedthrough lines 30 and-32 through reboiler 3l back to fractionator 25 to provide the heat for distillation and proper redux for the operation of fractionator or the bottoms may be recycled to the isomerization reactor 5 through preheater 4 `by means of line/34, but'if through inadvertence thejheater 8 is operated under too high a temperature orjthe hydrocarbon mixture subjected to the` temperature is maintained thereat too long, a heavy cracking occurs and excessive degrada` tion products are to be found in the bottom of. fractionator 25. In this case, outlet line 33 is provided for the removal of n-butane and degradation products for separate treatment to effectively4 remove" the heavy degradation products i prior tothe recycling of n-butane to preheater 4 or additional heat may be supplied. thereto in or- I der to substantially remove `from the desired hydrocarbons, through line II, the hydrogen chloride, hydrogen, if present, and any light products of thereaction, that is, those boiling below isobutane. All of these overhead eiiuents may be at least partially or completely removed from the system through line I2',` if desired. Generally, however, it is preferred to recycle the overhead until the degradation products (C2 and C3 hydrocarbons) havebecomebuilt up in amount excessively. Even when they `are partially withdrawn through line I2 a separate treatment to segregate hydrogen and/or hydrogen chloride for reuse in the unit may oftentimes be desirable. The withdrawals and additions through line `I2 are usually of intermittent character and designed purely to maintain a balanced operation.

The bottomsfrom stripper I0 are passed either directly into chiller I5 equipped withthe cooling jacket IB by means of line I4 or the bottoms from stripper I0 may be conducted through line I8 into heat interchanger I8 and from thence into cooler I5 by means of line 2| where any traces of aluminum chloride maybe separated out and removed from the system through the outlet 26 of chillerI5` The cooled `liquid is then conducted either directly to fractionator 25 by means of line I1 orithrough line 22 back into heat exchange relationship in heat interchanger, I8 'with the incomingbottoms from stripper I0 land thence from line `2II into fractionator 25. Fractionator 25 is ordinarily designed with some 50 or 60 plates and has a reflux recycle line at or near its top (not shown in the drawing) and a reboiler at or near its bottom. It is maintained under a temperature between about' 100 F. and 150 F. and under a pressure of .between about 50 and about 250 lbs. per square inch in order to effectively separate isobutane from n-butane. Ihe bottoms in fractionator 25 and consisting chiefly of n-bu- `tane are withdrawn from line 29 and may be diand reactor 5.

The drawing has been described with reference to theuse of a single reactor and n-butane as the feedstock."A It `is of course understood that the reactormay contain a mixture of normal paraflins of at least 4 carbon atoms per molecule. Likewise. the reactor maycomprise a series of reactors either arranged inseries or in parallel so that while one catalyst bed is being regenerated or replenished, the other 2 or 3 reactors remain on stream thereby providing 'a continuous isomerization reaction. Provision may also be made for the substantially continuous or semi-continuous addition of `aluminum chloride to the top of the reactor with the removal of a like volume of spent or substantially spent catalyst from the bottom thereof `so that a single reactor is constantly being catalyst is retained in the reaction zone for the longest periodof time and the subsequent heating ofthe eflluent containing the entrained and dissolved catalyst to the elevated temperatures, heretofore described, accomplishes the greatest economieswith respect to the greater overall catalytic s activity of the aluminum chloride, this latter type process is the preferred procedure.

As illustrative as to the character of the invention but withno `intention of limiting the inven-v tion thereto, the `following examples are given:

Example 1 sure'and the free feed rate to the tower of liquid n-butane was about 0.5 volume per volume of reaction space per hour. The eluent of the reaction vessel was heated with steam to a temperature of about 200 I'. as it passed to the subsequent recovery system,` During afizfhourrumthelyield;

of.y visoloutane amounted to. about, 3.31%

` EfrctmpleZy Nf-butaneV having the. same composition; as. that: specied inExample 1 had mixed. therewith.. about 1.7% by weight of hydrogenchloride andthemix.- ture was thenlpreheated tothe sameftemperature and pressure as speciiied in EixampleA 1 andi chargedV toI the `same. reaction vessel` as. described therein. The reactor was substantially. filledas before statedwith aluminum chloride powderand the nebutane mixture, was. charged; at` the same rate.- The eiluent from. the reactor Awasheated with steam. under pressure so that the temperature of theproducts was increased toabout 250? F. before being discharged therefrom for subsequent vtreatment and product recovery. The yield of l solid aluminum. chloride and consisting of the reaction products..y unreacted feed materials. and such amounts of aluminum -chloridelas haveloeenV dissolvedin the isomerization reaotion.zne, to. an. increased temperature for. aperiod of timesu.- cient to substantially completely utilize-the. activity of the dissolved aluminum. chloride in the hydrocarbon eiliuentV but fOr-less than. a suilcient. time toaccomplish substantialdegradation ofthe hydrocarbon mixture. so treated.

.2; A process. which comprisescontacting at leastone normal paraflin containingV at leastz4 carbon atoms per molecule underv isomerization reactionV conditions in the presence of a` solid. aluminum chloride catalyst mass anda halogen. containing promoter and-subjecting the-resultant hydrocarbon eiiluentas a mixturev substantially freeof solid aluminum chloride andconsisting of; the reaction products, unreactedfeed materials and suchlamountsof aluminum chloride as` have been dissolved inthe isomerizationreaction zone, to atleast a 25 F'. greater temperature than that under which the isomerization reaction was carried out for a period ottime-between about 5% and about 50% of the time of contact of the reaction mixture inthe isomerization reactionzone.

3; A rprocess asin claim 2 wherein the reaction is' carried out.v under superatmospheric.pressures sufcient to maintain a liquid phase operation under thereaction conditions obtained..

4. A process asin claim2 wherein the. reaction is carried out under. suicient superatmospheric pressure.. to maintain the hydrocarbon in the liquid phase under the reaction .conditions ola-- tained and wherein at least. a` portion of the superatmospheric pressure is ,maintainedr by reason of the. partial pressure. of molecular hydrogen in.. the, reaction zone. l

5.. A process.. y.which comprises contacting.A

nrbutane under'- a. temperature of:` between i about 150 and 27.59F. in'.` an ..isomerization. reaction zone: fora period off time between about. one.I and.

about. four hours iny the.` presenceof between hydrocarbon mixture,` subjecting the.` latter. asta mixture, consisting of the reaction products, un,.- reacted feed materials'and such amountsofalu.- minum;A chloride. as; havev been. dissolved 1n.` the isomerization. reaction zone, to. a temperature be.- tween about- 25 F. and 200 F. higher than-.they temperature maintained inr the-isomerizationree action zone for a period of time between about 10% and25% of the period of time-maintained in= the. isomerization reaction zone; andrecoverlng isobutane from the so treated` hydrocarbon: mixture.

6.. A. process which comprises contacting n-pentane under a temperatureyof-between;A about 2091i'.v and about 175 F. in` an isomerizationir reaction zone-ioll aperiod of; time` between about 0:55 and about 3 hoursin thepresence of between` about 2% and about 25%A of hydrogen chloride in thepresenceoi` between about.10.% and about 400% of. solid aluminum chloride andv` removing the reacted hydrocarbon mixture substantially free. of solidV material, subjecting the. reacted mixture; as; av mixture consisting of` theA reaction.

products,` unreacted feed materials. andi such amountsof aluminum chloride` as; have beendis.- solved in the isomerization. reaction; zone,. to -a temperatureV between about. 25' F. and 200W-F.v highergthanthe temperature maintained in. thev isomerization reaction zone for a period' of;y time between about, 10% and 25% of. the period of. time maintained inA they isomer-ization reaction Zonel and recovering. isopentane from; the: soi treated hydrocarbon mixture.

'Il A. process. which comprises subiectingf an; ef:- iiuent from an` isomerization reaction of; normal paraiin hydrocarbons with solidl aluminumy clilo'-y ride, which is substantiallyfree ofisolidaluminum. chloride and which consists of the reactionA products,a.unreacted feedmaterials and such amounts of.' aluminum chloride.. as have been'vdissolved: inV the isomerization reaction zone, to a temperature ofY from between about 25 Fpandabout 200 F. more than the hydrocarbons were sub. jected to insaid isornerizationr reaction..

BLA process. as in claiin'l wherein. theiin-1 creased temperature ranges. between about 50 F. and about/ F. morethan that maintained. inf said isomerization reaction.

9. A` vprocess which comprises f contacting n-butane containing# about 17 of its weightof. hydrogen chloride at a temperature'y of about F. and under a pressure of. about 400'rpounds perl square inch at'. a throughput of; about 0.5 v.'/v;/hr;. with aluminum chloride powder and subjecting thehydrocarbon eiiluent asa. mixture.-

` substantially freeV of entrained solidA aluminum;

chloridev and consisting'of the reaction pro.duct-s,. unreacted feed materialsV and.. such amountsof aluminumv chloride as. havebeen dissolved; in vthe' isomerization reaction zone, to .a temperature ofrabout250 E. prior. to the recoveryfof theisobutane from thereactantmixture.. f

RALPH BURGESS. MASON. 

